It has been a continuing problem in the art to develop simple and inexpensive methods of producing representations, or images, of repetitive, wide-bandwidth signals. The problem is exemplified in the oscilloscope art where analog oscilloscopes, for example, may operate on input waveforms having a bandwidth of approximately 500 or less megahertz, but only at high cost. This means that inexpensive analog oscilloscopes are limited to use with lower frequency waveforms.
The bandwidth characteristics of oscilloscopes was significantly advanced during the 1950s by the introduction of the sampling oscilloscope which can be generally classified as an instrument for generating representations of repetitive waveforms. The conventional sampling oscilloscope uses analog structure to store an analog potential proportional to the magnitude of a waveform point. A different waveform point is examined on each successive repetition of a repetitive waveform and the stored potentials of the sampled points are used to vertically deflect a cathode ray tube beam along a horizontal axis corresponding to time to produce an overall waveform representation or image. Low charge-density storage, fast switching diodes, operated at the appropriate time in relation to an occurrence of the waveform, are used to define each waveform point being sampled. Sampling pulses operate the diodes at the appropriate times. This, in turn, allows a storage circuit to charge to a potential proportional to the magnitude of the waveform at the sampled point.
The width of the sampling pulses determines the bandwidth characteristics of such analog sampling circuits. Typically, fast snap-back diodes are used to generate narrow pulses in order to achieve bandwidth characteristics having a current upper limit of about 2 gigahertz.
Although conventional analog sampling circuits, such as described above, are highly satisfactory and useful, the circuitry required to obtain such bandwidth characteristics is highly sophisticated and expensive. Thus, it is a continuing problem to find a sampling method and structure having wide-bandwidth characteristics and yet requiring nonsophisticated and inexpensive circuitry.